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  • 1
    ISSN: 0949-877X
    Keywords: Key words:Object-oriented modeling concepts – Consistency control – Query processing – Run-time optimization – Client/server architectures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. The increasing power of modern computers is steadily opening up new application domains for advanced data processing such as engineering and knowledge-based applications. To meet their requirements, concepts for advanced data management have been investigated during the last decade, especially in the field of object orientation. Over the last couple of years, the database group at the University of Kaiserslautern has been developing such an advanced database system, the KRISYS prototype. In this article, we report on the results and experiences obtained in the course of this project. The primary objective for the first version of KRISYS was to provide semantic features, such as an expressive data model, a set-oriented query language, deductive as well as active capabilities. The first KRISYS prototype became completely operational in 1989. To evaluate its features and to stabilize its functionality, we started to develop several applications with the system. These experiences marked the starting point for an overall redesign of KRISYS. Major goals were to tune KRISYS and its query-processing facilities to a suitable client/server environment, as well as to provide elaborate mechanisms for consistency control comprising semantic integrity constraints, multi-user synchronization, and failure recovery. The essential aspects of the resulting client/server architecture are embodied by the client-side data management needed to effectively support advanced applications and to gain the required system performance for interactive work. The project stages of KRISYS properly reflect the essential developments that have taken place in the research on advanced database systems over the last years. Hence, the subsequent discussions will bring up a number of important aspects with regard to advanced data processing that are of significant general importance, as well as of general applicability to database systems.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The VLDB journal 8 (1999), S. 25-43 
    ISSN: 0949-877X
    Keywords: Key words:Heterogeneity – Legacy systems – Mapping language – Schema integration – Schema mapping – Updatable views
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. This paper focuses on the problems that arise when integrating data from heterogeneous sources in a single, unified database view. At first, we give a detailed analysis of the kinds of structural heterogeneity that occur when unified views are derived from different database systems. We present the results in a multiple tier architecture which distinguishes different levels of heterogeneity and relates them to their underlying causes as well as to the mapping conflicts resulting from the view derivation process. As the second essential contribution, the paper presents our approach to a mapping language solving the identified conflicts. The main characteristics of the language are its descriptiveness, its capability to map between schemas written in the relational, object-oriented, ER, or EXPRESS data model, and its facilities for specifying user-defined update operations on the view that are to be propagated to the data sources. Finally, we briefly discuss how this mapping information is employed to convert queries formulated with respect to the integrated view, into database operations over the heterogeneous data sources.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The VLDB journal 5 (1996), S. 196-214 
    ISSN: 0949-877X
    Keywords: Key words: Referential integrity – Relational databases – SQL2 – MATCH clause – Access path support
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract. The relational model of data incorporates fundamental assertions for entity integrity and referential integrity. Recently, these so-called relational invariants were more precisely specified by the new SQL2 standard. Accordingly, they have to be guaranteed by a relational DBMS to its users and, therefore, all issues of semantics and implementation became very important. The specification of referential integrity embodies quite a number of complications including the MATCH clause and a collection of referential actions. In particular, $\hbox{{\tt MATCH PARTIAL}}$ turns out to be hard to understand and, if applied, difficult and expensive to maintain. In this paper, we identify the functional requirements for preserving referential integrity. At a level free of implementational considerations, the number and kinds of searches necessary for referential integrity maintenance are derived. Based on these findings, our investigation is focused on the question of how the functional requirements can be supported by implementation concepts in an efficient way. We determine the search cost for referential integrity maintenance (in terms of page references) for various possible access path structures. Our main result is that a combined access path structure is the most appropriatefor checking the regular MATCH option, whereas $\hbox{{\tt MATCH PARTIAL}}$ requires very expensive and complicated check procedures. If it cannot be avoided at all, the best support is achieved by a combination of multiple $\mbox{B}^*$ -trees.
    Type of Medium: Electronic Resource
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